Motorized apparatus for opening and closing sectional overhead doors has long been known in the art. These powered door operators were developed in part due to extremely large, heavy commercial doors for industrial buildings, warehouses, and the like where opening and closing of the doors essentially mandates power assistance. Later, homeowners' demands for the convenience and safety of door operators resulted in an extremely large market for powered door operators for residential usage.
The vast majority of motorized operators for residential garage doors employ a trolley-type system that applies force to a section of the door for powering it between the open and closed positions. Another type of motorized operator is known as a “jack-shaft” operator, which is used virtually exclusively in commercial applications and is so named by virtue of similarities with transmission devices where the power or drive shaft is parallel to the driven shaft, with the transfer of power occurring mechanically, as by gears, belts, or chains between the drive shaft and a driven shaft, normally part of the door counterbalance system, controlling door position. While some efforts have been made to configure hydraulically or pneumatically-driven operators, such efforts have not achieved any substantial extent of commercial acceptance.
The well-known trolley-type door operators are normally connected directly to the top section of a garage door and for universal application may be powered to operate doors of vastly different size and weight, even with little or no assistance from a counterbalance system for the door. Since the operating force capability of trolley-type operators is normally very high, force adjustments are normally necessary and provided to allow for varying conditions and to allow the operator to be tuned, depending on the application. When a garage door and trolley-type operator are initially installed and both adjusted for optimum performance, the overhead door system can perform well as designed. However, as the system ages, additional friction develops in door and operator components due to loss of lubrication at rollers and hinges. Also, the door can absorb moisture and become heavier, and counterbalance springs can lose some of their original torsional force. These and similar factors can significantly alter the operating characteristics seen by the operator, which may produce erratic door operation such as stops and reversals of the door at unprogrammed locations in the operating cycle.
Rather than ascertaining and correcting the conditions affecting door performance, which is likely beyond a homeowner's capability, or engaging a qualified service person, homeowners frequently increase the force adjustment to the maximum setting. However, setting an operator on a maximum force adjustment creates an unsafe condition in that the operator becomes highly insensitive to obstructions. In the event a maximum force setting is effected on a trolley-type operator, the unsafe condition may also be dramatically exemplified in the event of a broken spring or springs. In such case, if the operator is disconnected from the door in the fully open position during an emergency or if faulty door operation is being investigated, one half or all of the uncounterbalanced weight of the door may propel the door to the closed position with a guillotine-like effect.
Another problem with trolley-type door operators is that they do not have a mechanism for automatically disengaging the drive system from the door if the door encounters an obstruction. This necessitates the considerable effort and cost which has been put into developing a variety of ways, such as sensors and encoders, to signal the operator controls when an obstruction is encountered. In virtually all instances, manual disconnect mechanisms between the door and operator are required to make it possible to operate the door manually in the case of power failures or fire and emergency situations where entrapment occurs and the door needs to be disconnected from the operator to free an obstruction. These mechanical disconnects, when coupled with a maximum force setting adjustment of the operator, can readily exert a force on a person or object which may be sufficiently high to bind the disconnect mechanism and render it difficult, if not impossible, to actuate.
In addition to the serious operational deficiencies noted above, manual disconnects, which are normally a rope with a handle, must extend within six feet of the floor to permit grasping and actuation by a person. In the case of a garage opening for a single car, the centrally-located manual disconnect rope and handle, in being positioned medially, can catch on a vehicle during door movement or be difficult to reach due to its positioning over a vehicle located in the garage. Trolley-type door operators raise a host of peripheral problems due to the necessity for mounting the operator to the ceiling or other structure substantially medially of and to the rear of the sectional door in the fully open position.
Operationally, trolley-type operators are susceptible to other difficulties due to their basic mode of interrelation with a sectional door. Problems are frequently encountered by way of misalignment and damage because the connecting arm of the operator is attached directly to the door for force transmission, totally independent of the counterbalance system. Another source of problems is cause by the necessity for a precise, secure mounting of the motor and trolley rails which may not be optimally available in many garage structures. Thus, trolley-type operators, although widely used, do possess certain disadvantageous and in certain instances even dangerous characteristics.
The usage of jack-shaft operators has been limited virtually exclusively to commercial building applications where a large portion of the door stays in the vertical position. This occurs where a door opening may be 15, 20, or more feet in height, with only a portion of the opening being required for the ingress and egress of vehicles. These jack-shaft operators are not attached to the door but attach to a component of the counterbalance system, such as the shaft or a cable drum. Due to this type of connection to the counterbalance system, these operators require that a substantial door weight be maintained on the suspension system, as is the case where a main portion of the door is always in a vertical position. This is necessary because jack-shaft operators characteristically only drive or lift the door from the closed to the open position and rely on the weight of the door to move the door from the open to the closed position, with the suspension cables attached to the counterbalance system controlling only the closing rate.
Such a one-way drive in a jack-shaft operator produces potential problems if the door binds or encounters an obstruction upon downward movement. In such case, the operator may continue to unload the suspension cables, such that if the door is subsequently freed or the obstruction is removed, the door is able to free-fall, with the potential of damage to the door or anything in its path. Such unloading of the suspension cables can also result in the cables coming off the cable storage drums, thus requiring substantial servicing before normal operation can be resumed.
Jack-shaft operators are normally mounted outside the tracks and may be firmly attached to a door jamb rather than suspended from the ceiling or wall above the header. While there is normally ample jamb space to the sides of a door or above the header in a commercial installation, these areas frequently have only limited space in residential garage applications. Further, the fact that the normal jack-shaft operators require much of the door to be maintained in a vertical position absolutely mitigates against their use in residential applications where the door must be capable of assuming essentially a horizontal position since, in many instances, substantially the entire height of the door opening is required for vehicle clearance during ingress and egress.
In order to permit manual operation of a sectional door in certain circumstances, such as the loss of electrical power, provision must be made for disconnecting the operator from the drive shaft. In most instances this disconnect function is effected by physically moving the drive gear of the motor out of engagement with a driven gear associated with the drive shaft. Providing for such gear separation normally results in a complex, oversized gear design which is not compatible with providing a compact operator which can feasibly be located between the drive shaft for the counterbalance system and the door. Larger units to accommodate gear design have conventionally required installation at or near the end of the drive shaft which may result in shaft deflection that can cause one of the two cables interconnecting the counterbalance drums and the door to carry a disproportionate share of the weight of the door.
Another common problem associated particularly with jack-shaft operators is the tendency to generate excessive objectionable noise. In general, the more components, and the larger the components, employed in power transmission the greater the noise level. Common operator designs employing chain drives and high speed motors with spur gear reducers are notorious for creating high noise levels. While some prior art operators have employed vibration dampers and other noise reduction devices, most are only partially successful and add undesirable cost to the operator.
Another requirement in jack-shaft operators is mechanism to effect locking of the door when it is in the closed position. Various types of levers, bars and the like have been provided in the prior art which are mounted on the door or on the adjacent track or jamb and interact to lock the door in the closed position. In addition to the locking mechanism which is separate from the operator there is normally an actuator which senses slack in the lift cables which is caused by a raising of the door without the operator running, as in an unauthorized entry, and activates the locking mechanism. Besides adding operational complexity, such locking mechanisms also introduce an additional undesirable cost to the operator system.